Suck back valve



FIG. 1 shows a front view of a suck back valve showing my new design;

FIG. 2 shows a rear view thereof;

FIG. 3 shows a right side view thereof;

FIG. 4 shows a left side view thereof;

FIG. 5 shows a top view thereof;

FIG. 6 shows a bottom view thereof; and,

FIG. 7 shows a top, front and left side perspective view thereof. 

The ornamental design for a suck back valve, as shown and described. 